We developed the mass production procedure of Diaeretiella rapae, a biological control agent against pest aphids. Twenty female adults of D. rapae were introduced into a cage containing Lipaphis erysimi on two plants of komatsuna Brassica rapa nothovar. kept at 20[degree]C and a 15L-9D light cycle. Five treatments were used (i.e., 50-A, 100-A, 50-B, 75-B, 100-B); differing in the number of viviparous female adults provided (50, 75, 100) and interval between introduction of aphids and parasitoids (A: 0 day, B: 3 days). The newly mummified aphids (mummies) were counted and removed on days 7-9, 13-15 and 18-20 after aphid release, and the emergence rate and sex ratio of the parasitoids were assessed by rearing the mummies under the same conditions. From these results, the number of female parasitoids produced was calculated to be largest in 50-B (768), followed by 75-B (719), 100-A (584), 50-A (446) and 100-B (400). A simulation model for producing mummies developed from the life history traits of D. rapae and L. erysimi was used to analyze the present results. Diaeretiella rapae (Aphidiidae) : Parasite Lipaphis erysimi (Aphidoidea) : Host Animals and man; Control; Biological control; Techniques; Care in captivity; Parasites diseases and disorders; Parasites; Insect parasites; Hosts; Insect hosts Diaeretiella rapae; Control of; Lipaphis erysimi (Hemiptera); Rearing techniques; Hemipteran hosts; Mass production procedure for pest biocontrol agent; Lipaphis erysimi Lipaphis erysimi; Control by; Diaeretiella rapae (Hymenoptera); Hymenopteran parasites; Mass production procedure for pest biocontrol agent; Diaeretiella rapae none